Flickering Headlights
- Thread starter LAGA
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Interesting comment. Good info about the multimeters. Trav's article mentions problems attributable to rogue ac. Perhaps Benzes don't use ac filters on their electronics?
Regarding vehicle messy electrical systems and filtering-is this your opinion or is it referenced somewhere we can access? Would much appreciate this info.
Regarding vehicle messy electrical systems and filtering-is this your opinion or is it referenced somewhere we can access? Would much appreciate this info.
JHZR2
Staff member
Rectifying the three phase AC source in an alternator results in a DC waveform something like is shown in the below picture:
The ripple is the difference between the design equation: Vdc = root(2) * Vrms , and the minimum voltage, which is Vmin=Vdc sin (60).
Somewhere around 14%. So the battery has to "filter" this to provide what looks like a true flat line DC voltage.
If that does not happen, namely because the battery cannot filter all the ripple due to a high impedance or low capacity, there is the opportunity to observe flicker.
A busted diode would cause a greater peak to average, this image indicates why/the difference:
As you can see, a single sine wave makes for some very peaky DC, while three phases allow the "bumps" to have a higher frequency as each phase overlays the next. Of course, this means more consistent voltage, which also means less variable current. Again, bad battery, fluctuating current into high impedance means it cant filter well...
So a bad diode is a good basis for flicker, as is a bad battery...
The ripple is the difference between the design equation: Vdc = root(2) * Vrms , and the minimum voltage, which is Vmin=Vdc sin (60).
Somewhere around 14%. So the battery has to "filter" this to provide what looks like a true flat line DC voltage.
If that does not happen, namely because the battery cannot filter all the ripple due to a high impedance or low capacity, there is the opportunity to observe flicker.
A busted diode would cause a greater peak to average, this image indicates why/the difference:
As you can see, a single sine wave makes for some very peaky DC, while three phases allow the "bumps" to have a higher frequency as each phase overlays the next. Of course, this means more consistent voltage, which also means less variable current. Again, bad battery, fluctuating current into high impedance means it cant filter well...
So a bad diode is a good basis for flicker, as is a bad battery...
Yeh, it's why they're called alternators, not generators. Good post JHZR2.
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